Non-repeatable run out compensating apparatus and method and disc drive using the same

Abstract

An apparatus and method are provided for quickly and finely compensating for non-repeatable run out (NPRO) of a disc drive. The NPRO compensation control apparatus in a run out compensation apparatus of a system includes: a frequency estimator directly estimating a trigonometric function value of an NRRO frequency from a predetermined signal responding to the system using a correlation between a filter coefficient of a notch filter and a notch frequency; and an NRRO compensator canceling NRRO of the system using the trigonometric function value of the NRRO frequency estimated by the frequency estimator.

1. A non-repeatable run out (NRRO) compensation control apparatus in a run out compensation apparatus of a system, the apparatus comprising:
 a frequency estimator which directly estimates a trigonometric function value of an NRRO frequency from a predetermined signal responding to the system using a correlation between a filter coefficient of a notch filter and a notch frequency; and 
 an NRRO compensator which cancels NRRO of the system using the trigonometric function value of the NRRO frequency estimated by the frequency estimator. 
 
   
   
     2. The apparatus of  claim 1 , wherein the predetermined signal includes a position error signal (PES) generated according to head motion of a disc drive. 
   
   
     3. The apparatus of  claim 1 , further comprising a band pass filter which inputs the predetermined signal, passes only a band component in which it is possible for the NRRO to be generated, and outputs the band component to the frequency estimator. 
   
   
     4. The apparatus of  claim 1 , wherein the frequency estimator is initialized with a pre-known normal state value when starting. 
   
   
     5. The apparatus of  claim 1 , wherein the frequency estimator comprises:
 a finite impulse response (FIR) filter which filters the predetermined signal according to a predetermined frequency response characteristic; and 
 a tuner which inputs an output of the FIR filter and outputs a converged filter coefficient value while adjusting the filter coefficient in a direction where the output of the FIR filter is minimized. 
 
   
   
     6. The apparatus of  claim 5 , wherein a characteristic equation of the FIR filter is
     y ( n ) = x ( n )−2λ( n ) x ( n− 1)+ x ( n− 2) 
 where x(n) and y(n) are input and output signals of the FIR filter, respectively, and λ(n) is the filter coefficient. 
 
   
   
     7. The apparatus of  claim 5 , wherein the FIR filter is a notch filter. 
   
   
     8. The apparatus of  claim 5 , wherein the tuner adjusts the filter coefficient so that an output of the FIR filter is minimized using
   λ( n+ 1) =λ( n )+μ y ( n ) x ( n −1) 
 where λ(n) is the filter coefficient, x(n) and y(n) are input and output signals of the FIR filter, respectively, and μ is an adaptive gain constant. 
 
   
   
     9. A non-repeatable run our (NRRO) compensation control method in a run out compensation method of a system, the method comprising:
 directly estimating a trigonometric function value of an NRRO frequency from a predetermined signal responding to the system using a correlation between a filter coefficient of a notch filter and a notch frequency; and 
 compensating for NRRO of the system using the trigonometric function value of the NRRO frequency which is estimated. 
 
   
   
     10. The method of  claim 9 , wherein the predetermined signal includes a position error signal (PES) generated according to head motion of a disc drive. 
   
   
     11. The method of  claim 9 , wherein the predetermined signal is a band-pass-filtered signal including only a frequency band component in which it is possible for the NRRO to be generated. 
   
   
     12. The method of  claim 9 , wherein the trigonometric function value of the NRRO frequency is estimated with a convergence value of a filter coefficient adjusted to minimize an output signal of a variable coefficient finite impulse response (FIR) filter using the variable coefficient FIR filter. 
   
   
     13. A disc drive in a data storage system, the disc drive comprising:
 a state estimator which estimates a state information value of head motion including head position, velocity, and control input information from a position error signal (PES); 
 a state feedback controller which generates state feedback control information obtained by multiplying the state information value by a predetermined state feedback gain; 
 a non-repeatable run out (NRRO) compensation circuit which directly estimates a trigonometric function value of an NRRO frequency from the PES using a correlation between a filter coefficient of a notch filter and a notch frequency and generates NRRO compensation information corresponding to the estimated trigonometric function value of the NRRO frequency; 
 a summing unit which adds the NRRO compensation information to the state feedback control information; and 
 a voice coil motor (VCM) driver and actuator which moves a bead by generating a driving current corresponding to an output of the summing unit and generates the PES. 
 
   
   
     14. The disc drive of  claim 13 , wherein the NRRO compensation circuit comprises:
 a band pass filter which inputs the PES and passes only a frequency band component in which it is possible for the NRRO to be generated; 
 a frequency estimator which directly estimates the trigonometric function value of the NRRO frequency from an output of the band pass filter; and 
 an NRRO compensator which generates the NRRO compensation information using the trigonometric function value of the NRRO frequency estimated by the frequency estimator. 
 
   
   
     15. The disc drive of  claim 14 , wherein the frequency estimator is initialized with a pre-known normal state value when starting. 
   
   
     16. The disc drive of  claim 14 , wherein the frequency estimator comprises:
 a finite impulse response (FIR) filter which filters an output of the band pass filter according to a predetermined frequency response characteristic; and 
 a tuner which inputs an output of the FIR filter and outputs a converged filter coefficient value while adjusting the filter coefficient in a direction where the output of the FIR filter is minimized. 
 
   
   
     17. The disc drive of  claim 16 , wherein a characteristic equation of the FIR filter is
     y ( n )= x ( n )−2λ( n ) x ( n− 1)+ x ( n− 2) 
 where x(n) and y(n) are input and output signals of the FIR filter, respectively, and λ(n) is the filter coefficient. 
 
   
   
     18. The apparatus of  claim 16 , wherein the FIR filter is a notch filter. 
   
   
     19. The disc drive of  claim 16 , wherein the tuner adjusts the filter coefficient so that an output of the FIR filter is minimized using
   λ( n +1)=λ( n )+μ y ( n ) x ( n −1) 
 where λ(n) is the filter coefficient, x(n) and y(n) are input and output signals of the FIR filter, respectively, and μ is an adaptive gain constant.